1. Field of the Invention
The present invention relates to a tension apparatus for a sheet feeder machine. More particularly, the present invention relates to an improved tension apparatus for providing spring pressure in the second conveyor system of an envelope feeder. The envelope feeder is of a type used in combination with certain types of offset printers.
2. Prior Art
It is common in the print industry to provide offset presses and printers with sheet feed machines. These sheet feed machines provide a more efficient means of loading individual sheets of material such as envelopes, book pages and the like into an output feed or delivery station. Heretofore, a stack of envelopes, for example, was placed on top of a printer elevator of an offset press from which the top sheet was lifted off the stack by means of suction cups to be fed into the printer. The procedure continued until the stack was exhausted, thus requiring manual replacement of a new stack onto the printer elevator. This manual replacement was time consuming and inefficient.
Feeder machines have been provided to eliminate the above costly waste of man hours. The feeders are provided with a horizontal feed tray or table which acts as an output station and which is received into the input station or printer elevator of the printer. The machines are also provided with their own sheet input station, so that the sheet material can be continually replenished during the printing operation without needing to stop either machine. A intermediate conveyor mechanism comprising a plurality of rollers or hold down assemblies is used to move a stream of sheets atop a conveyor belt toward the output delivery station of the feeder.
Currently, the above intermediate conveyor mechanism is provided with an apparatus to adjust the downward pressure against the stream of sheets. This is a desirable feature since the size and thickness of the envelopes, as well as the speed of the operation can vary. The above variations can require adjustments in the pressure. However, the current method used to adjust the mechanism is clumsy and inefficient. A spring tension arm, which is attached at one end to a spring, is located on a inner side wall of the feeder. The other end of the tension arm is rotatably mounted on a rod which provides pivotal mounting for the above mechanism. In order to provide the correct downward spring pressure, an operator must push down on the tension arm while simultaneously loosening or tightening a thumb screw at the top of a portion of the above mechanism. This adjustment requires that the feeder machine be turned off.
A preliminary search was conducted on the present invention, and the following U.S. Pat. Nos. were uncovered:
2,012,130, 2,613,706, 3,942,789, 4,163,550, 4,445,668.
A prior art reference, U.S. Pat. No. 4,369,959 to Hornbuckle, discloses a sheet feed machine which comprises a sheet input station that can be continually replenished, an inversion station to invert a stream of sheets onto a conveyor system, and an intermediate conveyor mechanism to move a stream of sheets along the conveyor system toward the output delivery station. The intermediate conveyor mechanism is provided with a tension spring arrangement mounted on the central roller assembly. The Hornbuckle patent does not disclose an apparatus to adjust the tension on the forward and rear roller assemblies.
Another prior art reference, U.S. Pat. No. 4,163,550 to Armstrong, discloses pressure rollers mounted on parallel rods above a conveyor belt. The pressure rollers are individually adjusted and are of the type used to move sheets along conveyor belts after the printing operation. The other above mentioned prior art patents are not anticipatory to the present invention. No prior art reference discloses a tension apparatus that provides a quick and efficient means for adjusting the tension or pressure of the overall intermediate conveyor mechanism. No prior art reference discloses a tension adjustment apparatus that can be employed without needing to turn off the feeder machine.